Vanessa Hudgens walked the red carpet at Neutrogena's 2nd Annual Wave for Change By Helping Kids Make A Difference bash in Los Angeles on Monday -- and debuted a choppy, super-short new haircut! (She modeled her shaggy pixie alongside Hayden Panettiere, who lopped off her own locks earlier this year.)

Hudgens first revealed her major hair makeover on Thursday on the Newark, N.J., set of her new film "Gimme Shelter" (at left). The normally glammed-up star, 22, was unrecognizable in baggy, sloppy clothes, no makeup plus eyebrow and lip piercings.

In that film, she plays a pregnant teen forced to live on the streets.